In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be planarized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.
Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, using a polishing apparatus, while a polishing liquid containing abrasive particles such as silica (SiO2) or ceria (CeO2) therein is supplied onto a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing pad, so that the substrate is polished.
The polishing apparatus (CMP apparatus) for performing the above CMP (chemical mechanical polishing) process includes a polishing table having a polishing pad, and a substrate holding device, which is referred to as a carrier or a top ring, for holding a substrate such as a semiconductor wafer. By using such a CMP apparatus, the substrate is held and pressed against the polishing pad under a predetermined pressure by the substrate holding device, thereby polishing an insulating film, a metal film or the like on the substrate.
After one or more substrates have been polished, abrasive particles or ground-off particles of the substrate are attached to the surface of the polishing pad, and surface configuration or surface condition of the polishing pad is changed, resulting in deterioration in polishing performance. Therefore, as the substrates are repeatedly polished by the same polishing pad, a polishing rate is lowered and nonuniform polishing action is caused. Thus, dressing (conditioning) of the polishing pad is performed by using a dresser to regenerate the surface topography or surface condition of the polishing pad which has deteriorated.
In general, the CMP apparatus does not have a function for measuring surface properties such as surface topography or surface condition of the polishing pad directly. Therefore, there have been attempts to predict surface properties of the polishing pad by measuring the friction between the polishing pad and the substrate or between the polishing pad and the dresser indirectly. In this case, as a means for measuring the friction indirectly, it is common practice to reference a load torque of a motor for rotating the polishing table to which the polishing pad is attached.